Continuous coking process and apparatus



July 13, 1965 Filed Jan. 29, 1963 L. A. WINTER 3,394,753

CONTINUOUS COKING PROCESS AND APPARATUS 2 Sheets-Sheet l 69 ||l| Ill" 55INVENTOR.

LAWRENCE A. WINTER A T TORNEV L. A. WENTER 2 Sheets-Sheet 2 Filed Jan.29, 1963 INVENTOR LAWRENCE A. WINTER A TTORNEY United States Patent3,194,753 CQNTHNUQUE") CGKKNG PRGCESS AND APPARATUS Lawrence A. Winter,St. Albans, W. Va, assignor to Union Carbide Corporation, a corporationof New York Fiied Jan. 29, 1963, Ser. No. 254,643 4 Claims. (Cl. 2846)This invention relates to a method and apparatus for continuouslyproducing coke from thermally polymerizable hydrocarbon fractions, suchas pitch, asphalt, and tar.

Nearly all of the high quality, electrode-grade coke produced in theUnited States is made by a technique termed delayed coking in whichpolymerizable hydrocarbon residues are introduced into coking chambersat high temperatures and are polymerized therein without the benefit ofdirect heat by merely holding the said residues until coke formationtakes place and then periodically cooling and removing the hardenedcoke. The coking operation normally takes place at about 400 C. to 600C. at which temperatures the volatile components of the feed materialescape and the high-boiling components gradually polymerize, therebybeing transformed from a viscous liquid to a hard solid.

The major dificulty inherent in all known delayed coking processesresides in the fact that once the feed material has been fullypolymerized into hard coke it adheres to the vessel wall which makes itdifiicult to remove the coke from the coke drum or other coking vessel.The advances in the art of delayed coking have, therefore, centeredaround developing procedures for facilitating coke removal and cleaningof the coking vessel.

The labor requirement for cleaning the coke drums was greatly reduced bythe advent of cable pulling methods for coke removal. Cables weresupported in the clean drums by means of wires in a systematic fashion.Upon completion of the coking cycle the bottom closure of the drum wasremoved and the embedded cables pulled out of the drum with a poweredwinch. This pulling of the cables resulted in the coke falling out ofthe drums in chunks and left but a small portion of the drum to becleaned manually. The cable pulling method was a great advance in theart of delayed coking but installing the cables still requiredconsiderable labor and the cables had a limited life so that theindustry still desired a better method. The next major advance in theart was the development of hydraulic de-coking methods and equipment.This improvement replaced the cable pulling installations rapidly and istoday the standard oil industry coking system whenever delayed coking ispracticed. In such hydraulic techniques, coke is removed from the drumsby means of water jets which cut the body of coke into pieces smallenough to drop into a crusher car. A typical assembly is shown anddescribed by Maass et al. in Petroleum Processing, January 1947.

The delayed coking technique is not to be confused with the relativelynew fluidized bed and moving bed processes in which coking time is onlya few minutes and process heat is supplied continuously whereas, indelayed coking, coking times can approach a full day and the only sourceof heat is the enthalpy of the feed stream. Coke produced by the variousfluidized bed and moving bed processes is generally of fuel value onlyand not suitable for making electrodes.

As can be seen from the history of the delayed coking are, even the mostmodern techniques are still batch operations in which equipment must beperiodically shut down for coke removal, and thus are subject to theusual disadvantages inherent in discontinuous operation. For example,the coking unit is off stream for substantial periods of time and thusat least two units are necesice sary for handling a continuous stream offeed material as obtained from an oil refinery. In addition, theequipment used is exposed to alternating periods of high and lowtemperature and also, during hydraulic coke removal, to contact withwater and wet steam and therefore sub jected to great strain andcorrosion. Also inevitable in the known discontinuous processes is thenon-uniform quality of the coke produced as a result of variable cokingtimes for different segments of the polymerizing coke cylinder.

The present invention obviates or mitigates the abovementioneddifficulties and disadvantages by providing a simple, continuous delayedcoking process requiring only occasional control by an operator andcapable of producing coke of uniform and high, electrode-grade quality.

In essence, my invention comprises providing an annular layer ofpulverized coke separating a cylinder of a polymerizing mass comprisingpolymerizable hydrocarbon fractions from the inside surface of thecoking vessel and thereby acting as a sliding surface which preventsadherence of the polymerizing mass to the inside surface of the cokingvessel and permits the column of polymerizing mass to progresscontinuously downward.

The rate of descent of the column of polymerizing mass is convenientlycontrolledby fragmenting means supporting the said column andfragmenting the fully polymerized coke, preferably by a combined cuttingand wedging action.

In a preferred embodiment of this invention the annular layer ofpulverized coke proceeds downwardly at about the same rate as the columnof polymerizing mass and is recycled to the top of the coking vessel forrepeated use, loss of pulverized coke during descent being compensatedfor by so adjusting said fragmenting means as to provide the necessaryamount of pulverized coke to replenish the recycling pulverized cokestream.

A fuller understanding of the present invention and of an apparatussuitable for carrying out a preferred embodiment of the process of myinvention can be had by reference to the appended drawing wherein FIGURE1 is a vertical crosssection of the overall assembly utilizable in myinvention; and

FIGURE 2 is a perspective view of typical fragmenting means forming partof the apparatus of FIGURE 1. 7

With reference to FIGURE 1, the assembly comprises, as the majorcomponents, pre-coking vessel means 11, substantially cylindrical cokingvessel means 13 provided near the top thereof with bafiie means 15comprising a hollow inverted truncated cone disposed in coaxialrelationship with said coking vessel means 13, coke fragmenting means 17situated at the bottom of said coking vessel means 13. During steadystate continuous practice of my invention, a polymerizable feed streamis continuously introduced through line 19 and heated by heating meanssuch as pipe still heater 21 wherein the feed temperature is raised tothe preferred coking temperature. The hot feed stream is then led vialine 23 to pre-coking vessel means 11 wherein gases and vapors producedduring heating of the feed stream are allowed to escape through escapevalve means 25 and wherein some polymerization of the feed materialsoccurs, the extent of such polymerization being optionally ascertainedby viscosity measuring means 27. Feed material from pro-coking vesselmeans is controllably introduced through inlet valve means 29 to theupper portion of coking vessel 13. Simultaneously and continuouslyintroduced in a circumferentially distributive manner through inletports such as 31 and 33 is pulverized coke which is then directed to theperiphery of the inside surface of coking vessel 13 by batlle means 15to form an annular layer concentric with said coking vessel 13 andseparating a polymerizing mass35 of feed material from the insidesurface of said coking vessel 13. The annular layer of pulverized cokeextends from the top of the bottom of coking vessel 13 to form a hollowcylindrical substantially coaxial with the coking vessel 13 and filledwith the polymerizing mass and serving as a sliding surface to permit agradual descent of the polymerizing mass, the rate of descent beingcontrolled by fragmenting means 17. Fragmenting means 17 can compriseany suitable device known to those skilled in the coke-cutting artcapable of achieving a minimum of true cutting and a maximum of wedgingaction to produce a high percentage of lump coke and a minor amount ofpulverized coke. In the embodiment shown, fragmenting means 17 comprisescutter blades 51 extending radially and upwardly from shaft 53 which inturn is supported by thrust bearing 55 and turned by gear means 57 viapinion gear 59 by motor 61. A packing gland 63 provides a seal for theshaft 53 which is also stoutly held in place by hearing 55. Theconstruction of fragmenting means 17 is further illustrated in FIG- URE2 which is a perspective view thereof.

For cases in which shrinkage of the coke cylinders occurs duringpolymerization, causing the bottom end of said cylinder to be rotated bythe fragmenting device, such rotation can be avoided by providingsuitable means such as a plurality of circular sharply toothed gears 71the axes of which are at right angles to the axis of said descendingcoke cylinder, engaging the coke cylinder circumferentially near thebottom thereof, thereby preventing rotation of the coke cylinder and, inaddition, ensuring positive contact of the coke cylinder withfragmenting means 17. The coke lumps and coke fines produced byfragmenting means 17 drop down chute 81 onto screen 83 which directs thecoke lumps to a quenching and discharge system well-known to thoseskilled in the art of coke handling. The coke fines falling throughscreen 83 are collected in hopper 85 and are advantageously recycled viaconveying means 87 and recycle feed bin 89 to coking vessel 13 at pointssuch as 31 and 33. The conveying means 87 can be of any suitable typesuch as a gas lift, and controllable partial combustion of the cokefines can be provided to maintain the fines at a high temperature, ifsuch is advantageous for forming an effective pulverized coke layer inthe coking vessel.

The process as described above is a steady-state continuous one. In theoriginal start-up of the coking unit shown in the preferred embodiment adifferent procedure is required. The vessel is charged manually withmechanically assists from conventional handling devices well known tothose skilled in the art of solids handling. An expendable material suchas wood is used to form a temporary barrier facing the fragmenting means17 to prevent vapors from condensing in equipment below the fragmentingmeans 17 during the start up operation. Small lumps of coke are thenintroduced to coking vessel 13 by means of suitable flexible chutesthrough manholes such as 91. Pulverized coke is introduced through.inlet ports 31 and 33 and deposited around the vessel wall by means of aflexible hose while filling the bulk of the vessel with the small lumpcoke so that a cylindrical column, lined with a pulverized coke layer,is built up. When the bottom of baffle means is reached, additionalpulverized coke is added from feed bin 89 through ports 31 and 33 tofill the space between baflie means 15 and the coking vessel Walls. Thesystem is tested for gas tightness and the valving set to permit heatingof the feed material in coking vessel 13 with hot gas or superheatedsteam introduced near the bottom of vessel 13 at hot gas inlet 93. Theheating means 21 is available for this purpose by closing valve 95 andopening valve 97. The hot gas or superheated steam passes hot gas inlet93 and upward through the bed of coke lumps out the top of coking vessel13 and, with valves 29 and 25 open, also brings pre-coking vessel 11 tooperating temperature. An expendable tube can be utilized tointroduce'the heating gases into the middle of the bed of coke lumpswithout disturbing the pulverized coke layer near the hot gas inlet 93.Once the operating temperature has been reached the hydrocarbon feedstream is temporarily led through the same path as the heating gases,through heating means 21, valve 97 and inlet 93 into the center of thelump coke bed. The feed then 'percolates upward between the lumps ofcoke, filling any open spaces and eventually turning to coke. TheVolatile constituents of the feed continue upward to vessel 11 and bringthe entire system to full operating temperature. When the molten polymerreaches the top of the lump coke bed at the lower end of the bafilemeans 15 the hot hydrocarbon feed stream is switched to the top ofpre-coking vessel 11 by opening valve 95 and closing valve 97 and inlet93. Vessel 11 is allowed to partially fill by closing valve 29 so as toprovide'some residence time for partial polymeriza tion of the freshfeed while the feed previously introduced to coking vessel 13 ispermitted to coke fully by not being diluted with fresh feed.Fragmenting means 17 is then put into operation, valve 21 is actuated bysuitable instrumentation to control the flow of partially polymerizedheavy residuesfrom vessel 11 so as to maintain the proper level of thereaction mass in vessel 13. The .remainder of the equipment operatessubstantially as set forth above in the description of the continuousprocess.

Although operating campaigns on this continuous coker would be expectedto be quite long, eventual temporary shutdowns for maintenance purposesmust be anticipated. A shutdown would be performed by merely causing theflow of feed to cease by closing the proper valves, purging heatingmeans 21 and connected piping, draining the heavy residue from vessel 11to the top of the coking vessel 13, and continuing coke withdrawal fromfragmenting means 17 until the upper level of the heavy residue islowered to approximately the level of the bottom of the baffle means 15.Operation is thus stopped with the coking vessel full of coke and thefine coke barrier still in place. After such a shutdown, start-up iseasily accomplished. The upper portion of vessel 13 is heated byintroducing hot gas or super-heated steam through valve 95 into vessel11; valves 29 and 28 are kept open during this operation while valves 25and 26 are closed. Hot hydrocarbon feed is then started through heatingmeans 21 with valves 25 and 26 open and valves 29 and 28 closed. Asstated in the previous start-up description valve 29 is placed underautomatic control after vessel 11 becomes filled to a suitable level,fragmenting means 17 is put into operation, and pulverized cokerecirculated continuously.

The term pulverized coke as used herein is meant to include coke finesor coke breeze such as normally obtained in the coke industry as theresult of natural breakage in handling and consisting of coke ,as wellas anthracitic fines, coal dust, and the like. Coke fines are preferredin my process because they are essentially nonfusible upon reheating andthus ideal for barrier formation. It will be apparent that other fineinerts, such as sand, clay, or alumina, might serve in place of thepulverized coke, particularly in cases where some contamination of theresulting coke can be tolerated.

The thickness of the pulverized coke layer separating the polymerizingmass from the coking vessel wall, while not narrowly critical, must besufficient to prevent penetration of said polymerizing mass therethroughin order to aviod adherence of the coke to the vessel wall. Thethickness of the pulverized coke layer will therefore depend to someextent on the nature of the feed stream being processed. A feedcomprised mainly of heavy residues will be relatively viscous and havelittle tendency to penetrate through the coke barrier, while a feedcomprising lighter hydrocarbon fractions will be less viscous, requiringa thicker coke barrier. When processing coal hydrogenation pitch I havefound that coke layer thickness of one inch is sufiicient for forming aneffective barrier inasmuch as the pitch penetrates only up toone-quarter inch into the barrier.

The temperature of the pulverized coke can be the same as that of thepolymerizing mass or it can be higher or lower. Using a relatively coolpulverized coke layer may be advantageous in that the viscosity of thepolymerizing mass is extremely temperature-sensitive and increasesrapidly upon cooling. Thus, av pulverized coke layer slightly coolerthan the polymerizing mass would be even more impervious to penetrationthereby. On the other hand, in some applications it may be desirable tointroduce the pulverized coke at temperatures above that of thepolymerizing mass in order to cause more rapid coking of thepolymerizing mass that does penetrate, thereby providing a skin for thedescending coke cylinder. In such operation it is apparent that theintroduction of pulverized coke should be such as to permitsubstantially identical rates of downward progress for the pulverizedcoke and the polymerizing cylinder. However, in the general practice ofmy invention, such identical rates of downward progress are notessential, although preferred. In certain applications it may bedesirable to force-feed the pulverized coke at points such as 31 and 33in FIGURE 1, in order to ensure continuous movement of the barrierannulus. Suitable means of force-feeding would be gas pressure ormechanical means such as a ram or pusher.

It will be understood that the foregoing description has been given witha high degree of particularity so that those skilled in the art mayunderstand fully a preferred embodiment of this invention but that theinvention is in no sense limited thereto and variations in apparatus,materials, and operating conditions will be apparent to the skilledartisan.

While the embodiment shown is particularly adapted to processing ofpitch-like polymerizable hydrocarbons, my process is applicable tocoking of all types of thermally polymerizable hydrocarbon feeds, e.g.coal hydrogenation pitch, coal tar pitch, coal tar, asphalt, crude oil,heavy residuum, and various fractions thereof. If the feed containslow-boiling constituents, vessel 11 could be modified to function as afiash pot and serve to separate the lowboiling materials from thehigh-boiling compenents of the feed, the latter then being introducedinto the main coking vessel.

The following examples are illustrative.

Example I A hollow steel cylinder with an inside diameter of four inchesserved as the coking vessel in this experiment. A sheet metal stackhaving a diameter of three inches was placed inside the said cylinder incoaxial relationship therewith and the resulting cylindrically annularcavity between cylinder and stack was filled with pulverized coke,specifically, metallurgical coke ground so that 99.4 percent by weightpassed through an 8-mesh Tyler screen and 17.8 percent by weight passedthrough a ZOO-mesh screen. The thus-formed pulverized coke barrier was,therefore, onehalf inch thick. A charge of 500 grams of molten coalhydrogenation pitch (viscosity: 64,000 centipoises at 425 C.) was heatedto 425 C. and introduced into the cylindrical cavity formed by the saidsheet metal stack. The stack was then elevated at the rate of one inchper minute thereby allowing gradual contact of the molten pitch with thesaid pulverized coke barrier. After the stack was pulled out, theassembly was allowed to remain at 425 C. for six hours. After this timea cylinder of hard coke measuring 3% inches in diameter and 4 inches inheight and weighing 321 grams was easily removed from the assembly.Examination of the coke cylinder showed that the pitch had penetratedonly inch into the pulverized coke barrier.

Example II A hollow steel cylinder with an inside diameter of twelveinches served as the coking vessel in this experi ment. A sheet metalstack having a diameter of ten inches was placed inside the saidcylinder in coaxial relationship therewith and the resultingcylindrically annular cavity between cylinder and stack was filled withpulverized coke,

specifically, metallurgical coke ground so that 93.9 percent by weightpassed through an S-mesh Tyler screen and 9.6 percent by weight passedthrough a ZOO-mesh screen. The thus-formed pulverized coke barrier was,therefore, one inch thick. A charge of 40 pounds of molten coalhydrogenation pitch (viscosity 9,600 centipoises at 465 C.) was heatedto 465 C. and introduced into the cylindrical cavityforined by the saidsheet metal stack. The steel cylinder was then lowered at the rate ofone inch per minute with the stack remaining stationary, therebyallowing gradual contact of the molten pitch with the said pulverizedcoke barrier. After the stack was pulled out, the

assembly was allowed to remain at 465 C. for siX hours. After this timea cylinder of hard coke weighing 30 pounds was easily removed from theassembly. Examination of the coke cylinder showed that the pitch hadpenetrated from to A inch into the pulverized coke barrier.

Example 111 The experiment described in Example 11 was repeated usingmolten coal hydrogenation pitch having a viscosity of 20,000 centipoisesat 450 C. and heated to 450 C., and, to form the barrier, petroleum cokeground so that 100 percent by weight passed through an S-mesh Tylerscreen and 4.8 percent by weight passed through a 200- rnesh screen. Theresulting coke cylinder was completely free from the vessel wall andexamination showed that the pitch had penetrated only from to inch intothe barrier.

For purposes of comparison, a control experiment was carried out withoutuse of the coke barrier of this invention. A charge of 1600 grams ofmolten coal hydrogenation pitch was introduced into a steel cylinder sixinches in diameter and twelve inches high. A temperature of 460 C. wasmaintained for three hours. The apparatus was disassembled and the cokewas found to be firmly adhering to the cylinder wall. A hammer, chisel,scraper, and wire brush were necessary to clean the coking vessel.

Coke samples produced by known means as Well as by the process of thisinvention were evaluated side-by-side. The results of this evaluationare set forth below.

1000 C. Resis- Thermal Coking Apparent tanee Expansion, Value Density(Ohmin./in./ C.

inches) conventionally prepared colt 94. 02 1. 483 0. 000360 9. 8 l0-Coke from Ex inple I:

01) 91. 40 1. 541 0. 000357 11. 8Xl0- Bottom 90. 86 1. 541 0. 000341 9.7X10- Coke from Example II 92. l. 532 0. 000319 10. 7X10- Coke fromExample IIL..- 93. 00 1. 516 0.000337 10. 5 l0- Thus it is noted thatcoke produced by this invention equivalent in quality to coke producedfrom the same hydrocarbon feed by standard procedures.

What is claimed is:

:1. The method for continuously producing coke from thermallypolymeriza'ble hydrocarbon fractions which comprises introducing saidhydrocarbon fractions at coking temperatures into a substantiallycylindrical vertical coking chamber and maintaining an annular layer ofpulverized coke around the inside periphery of said coking chamber so asto separate the polymerizing hydrocarbon fraction from the wall-s ofsaid coking vessel, and continuously withdrawing hard coke at the bottomof said coking chamber.

2. The method for continuously producing coke from thermally polymerizable hydrocarbon fractions which comprises introducing said hydrocarbonfractions, at coking temperatures, into a substantially cylindricalvertical coking chamber while simultaneously introducing pulverized cokenear the top of said coking chamber in circ'umferentially distributivemanner to form an annular layer of pulverized coke around the insideperiphery of 7 said coking chamber so as to separate the polymerizinghydrocarbon fraction from the Walls of said coking vessel, andcontinuously withdrawing hard coke at the bottom of said coking chamber.

3. The method for continuously producing coke from thermallypolymeriza-ble hydrocarbon fractions which comprises introducing saidhydrocarbon fractions, at coking temperatures, into a substantiallycylindrical vertical coking chamber while simultaneously introducingpulverized coke near the top of said coking chamber, incircumferentially distributive manner to form an annular layer ofpulverized coke around the inside periphery of said coking chamber so asto separate the polymerizing hydrocarbon fraction from the Walls of saidcoking vessel, continuously withdrawing hard coke at the bottom of saidcoking, chamber, and continuously Withdrawing pulverized coke at thebottom of said coking chamber and re- 8 cycling said pulverizedcoke tothe top of said coking chamber for repeated use.

4. Apparatus for continuously coking thermally polymeriza-blehydrocarbon fractions comprising substantially cylindricalverticalcoking vessel means, bafile means situated near the top thereof capableof circumferenti-ally distributing pulverized coke to form an annularlayer of pulveriized coke'around the inside periphery of said cokingvessel, and coke fragmenting means situated near the bottom of saidcoking vessel means in operative cont act with a descending cylinder ofhard coke.

References Cited bytlle Examiner UNITED STATES PATENTS 1,864,686 6/32Fields f 208-126 2,114,416 4/38 Donnelly 20850 ALPHONSO D.sULLIvAmPrimar Examiner.

1. THE METHOD FOR CONTINUOUSLY PRODUCING COKE FROM THERMALLYPOLYMERIZABLE HYDROCARBON FRACTIONS WHICH COMPRISES INTRODUCING SAIDHYDROCARBON FRACTIONS AT COKING TEMPERATURES INTO A SUBSTANTIALLYCYLINDRICAL VERTICAL COKING CHAMBER AND MAINTAINING AN ANNULAR LAYER OFPULVERIZED COKE AROUND THE INSIDE PERIPHERY OF SAID COKING CHAMBER SO ASTO SEPARATE THE POLYMERIZING HYDROCARBON